1. Field of the Invention
The present invention relates to a motorcycle. More particularly, the invention relates to a motorcycle in which a damping element is used in a structural part for coupling left and right portions of a vehicle body frame to each other to thereby ensure that vibration characteristics (dynamic flexure characteristics) of the vehicle body can be adjusted.
2. Description of Background Art
In general, a vehicle body of a motorcycle is configured by a method in which members formed of metal, such as steel or a light alloy, are connected to each other by welding or coupling with screws. The maneuverability and ride quality of such a vehicle body can be adjusted to a certain extent by varying the rigidity of the vehicle body. However, the adjustment by varying the rigidity is an adjustment by varying the spring constant of the vehicle body. Since variations in damping characteristics of the vehicle body are slight even when the spring constant of the vehicle body is varied, it is difficult to adjust the damping characteristics by varying the rigidity of the vehicle body.
Thus, it is very difficult work to attain vibration characteristics of parts of the vehicle body suited to a plurality of running modes by only varying the spring constant of the vehicle body.
A conventional motorcycle is known, see for example Japanese Patent Laid-open No. Sho 62-137287, in which a vehicle body frame is provided with joint parts (15, 16) and a damping member (20) intermediately provided at the joint parts (15, 16), for the purpose of dispersing lateral vibrations generated in the vehicle body, reducing the amplitude of low-frequency vibrations and thereby achieving a further enhanced ride quality.
In this motorcycle, however, as seen in FIG. 2 in Japanese Patent Laid-open No. Sho 62-137287, the joint parts (15, 16) are provided only for the frames disposed on the left and right sides in the vehicle body, so that it is difficult to obtain vibration characteristics suitable for a plurality of running modes.
In addition, another conventional motorcycle is known, see for example Japanese Patent Laid-open No. 2007-145268, wherein an elastic coupling part (35) for coupling front and rear frame pipes (36, 37) as component members of a vehicle body frame (5) to each other through an elastic member (41) is provided at a part of the vehicle body frame (5).
In this motorcycle, however, as seen in FIG. 1 in Japanese Patent Laid-open No. 2007-145268, the elastic coupling part (35) is provided only for a frame disposed along the front-rear direction at the center of the vehicle body. Therefore, it is again difficult to obtain vibration characteristics suited to a plurality of running modes.
In addition, as set forth in Japanese Utility Model Publication No. Hei 03-040700 for example (the claims, and object paragraphs), a performance rod mounting structure for automobile is known, wherein rear end portions of the performance rods are opened wider toward the vehicle body front side substantially in the form of an obtuse “V” separated at the vertex thereof and are secured to vehicle body portions on the front side of the vehicle compartment. Further, front end portions of the performance rods are secured to vehicle body side portions. In such a performance rod mounting structure, vibrations from the engine and the suspension may be transmitted to the vehicle body portions on the front side of the vehicle compartment through the performance rods, possibly resulting in the generation of noise. More specifically, a booming noise in the vehicle compartment. In order to eliminate the possibility of the generation of the noise, in this mounting structure, a weight is attached to the rear end portions of the performance rods through elastic bodies, respectively, so that the weight and the elastic bodies form a dynamic damper.
According to this mounting structure, the generation of noise in the vehicle compartment can be suppressed by the action of the dynamic damper. Since the dynamic damper is only provided in the vehicle body, however, it is impossible to obtain vibration characteristics suited to a plurality of running modes.